Illustration Credit: Wageningen University & Research
Scientific Frontline: "At a Glance" Summary: Global Coastal Sea Level Assessments
- Main Discovery: Sea levels along global coastlines are significantly higher than previously assumed in coastal hazard impact studies, with actual levels in regions like Southeast Asia and the Indo-Pacific measuring 1 to 1.5 meters above prior baselines.
- Methodology: Researchers analyzed 385 recent scientific publications and calculated the true difference between coastal land elevation and actual sea level. They accurately integrated satellite-based sea level measurements with land elevation data, correcting the historical reliance on global geoid models.
- Key Data: Corrected calculations reveal that 37 percent more area and 68 percent more people, totaling up to 132 million individuals, will fall below sea level following a 1-meter relative sea-level rise. Over 90 percent of previous studies relied on inaccurate geoid models rather than actual sea level measurements.
- Significance: Previous models severely underestimated the physical exposure of coastal areas and populations worldwide. The hazardous impacts of sea-level rise will manifest much sooner than initially predicted, mandating an urgent reassessment of global coastal vulnerability.
- Future Application: The corrected methodology and newly available, ready-to-use coastal elevation datasets provide a precise standard for researchers and policymakers to deploy targeted coastal adaptation and protection strategies.
- Branch of Science: Earth Sciences, Geography, Oceanography
- Additional Detail: Global geoid models historically used for sea-level estimates rely entirely on Earth's gravity and rotation, failing to account for critical dynamic variables such as winds, ocean currents, tides, water temperature, and seawater salinity.
Studies on the effects of rising sea levels on coastal regions often refer to an assumed sea level instead of actual measured sea level. A German-Dutch research team provides a corrected calculation to reassess the consequences for coastal regions worldwide
Sea levels along the world’s coastlines are much higher than often assumed. In the most affected regions, like Southeast Asia and the Indo-Pacific, they are even around 1 to 1.5 meters higher than the level on which previous impact assessments for coastal hazards were based. This is shown by a study led by geographers Dr Philip Minderhoud (Wageningen University & Research) and Katharina Seeger (University of Cologne). The results suggest that the underlying methodology of almost all previous coastal hazards studies needs to be re-evaluated and, in most cases, updated.
Minderhoud and Seeger found that the majority of existing coastal impact studies use a reference sea level that is on a global average lower than the actual sea level along the coast. The researchers calculated the difference between coastal land elevation and sea level around the world and compared their results to 385 recent scientific publications. They found that more than 90 percent of these studies did not use sea level measurements but only land elevation measurements with their elevation referenced to so-called 'global geoid models’. These are models that provide an estimate of the global sea level based on the Earth’s gravity and rotation. “In reality, the sea level is influenced by additional factors such as winds, ocean currents, tides as well as the temperature and salinity of the seawater,” explains Minderhoud. “The actual amount may therefore differ.”
Satellites provide globally available measurements of both land elevation and sea level, the latter within an accuracy of just a few centimeters. “However, land and sea levels are measured using different satellites, often provided in relation to a different geoid, which doesn’t make it easy to combine the information,” says Seeger. “When we correctly integrated accurate sea level measurements with land elevation, we found that in many places around the world coastal sea levels are considerably higher than geoid models suggest.”
The team documents that in many impact studies, there is a mismatch between the assumed sea level and the actual measured sea level. “As a result, studies that do not properly account for actual sea level, underestimate the amount and exposure of coastal areas and their populations worldwide,” explains Seeger. “Our corrected calculations reveal that 37 percent more area and 68 percent more people – up to 132 million – will fall below sea level following 1 metre of relative sea-level rise than previous geoid-based assessments suggested.”
These findings could change perspectives on the need for coastal adaptation and protection measures. Minderhoud explains: “If the sea level is in reality higher than previously assumed, the impacts from sea-level rise in the affected regions will be occurring sooner than previously predicted.” It is still unclear how much the underestimations of coastal impacts in scientific studies have found their way into policy and its implementation. Seeger says: “To support future research, we provide all the methodological steps required to make the corrections to integrate sea level data and coastal land elevation. We also provide ready-to-use coastal elevation data for the entire world, in which the most recent sea level measurements are correctly integrated.” Minderhoud adds: “Now that we have uncovered this blind spot, we hope our methodology will become the new standard by which the global research community can create more accurate coastal assessments. This will help to determine which areas in the world are most affected by future sea-level rise and where coastal adaptation strategies are most urgently needed.”
Reference material: What if our sea-level rise impact assessments underestimate sea level? (video)
Published in journal: Nature
Title: Sea level much higher than assumed in most coastal hazard assessments
Authors: Katharina Seeger, and Philip S. J. Minderhoud
Source/Credit: University of Cologne
Reference Number: es030626_01